Since an infrastructure for supplying hydrogen has not been developed, a system, such as a fuel cell system, which uses the hydrogen as a fuel is normally provided with a reformer. In addition, the fuel cell system is provided with a combustor configured to heat the reformer.
Proposed is a fuel cell system in which a CO detector is disposed on an exhaust duct of the combustor such that carbon monoxide (CO) generated by, for example, incomplete combustion of the combustor can be detected (see PTL 1, for example). PTL 1 discloses a technology in which a water discharge portion disposed on the exhaust duct discharges dew condensation water in the exhaust duct to prevent the CO detector from being immersed in the dew condensation water.